1. Field
The present disclosure relates generally to data networking and in particular to a backhaul radio for connecting remote edge access networks to core networks in RF bands subject to uncoordinated interference.
2. Related Art
Data networking traffic has grown at approximately 100% per year for over 20 years and continues to grow at this pace. Only transport over optical fiber has shown the ability to keep pace with this ever-increasing data networking demand for core data networks. While deployment of optical fiber to an edge of the core data network would be advantageous from a network performance perspective, it is often impractical to connect all high bandwidth data networking points with optical fiber at all times. Instead, connections to remote edge access networks from core networks are often achieved with wireless radio, wireless infrared, and/or copper wireline technologies.
Radio, especially in the form of cellular or wireless local area network (WLAN) technologies, is particularly advantageous for supporting mobility of data networking devices. However, cellular base stations or WLAN access points inevitably become very high data bandwidth demand points that require continuous connectivity to an optical fiber core network.
When data aggregation points, such as cellular base station sites, WLAN access points, or other local area network (LAN) gateways, cannot be directly connected to a core optical fiber network, then an alternative connection, using, for example, wireless radio or copper wireline technologies, must be used. Such connections are commonly referred to as “backhaul.”
Many cellular base stations deployed to date have used copper wireline backhaul technologies such as T1, E1, DSL, etc. when optical fiber is not available at a given site. However, the recent generations of HSPA+ and LTE cellular base stations have backhaul requirements of 100 Mb/s or more, especially when multiple sectors and/or multiple mobile network operators per cell site are considered. WLAN access points commonly have similar data backhaul requirements. These backhaul requirements cannot be practically satisfied at ranges of 300 m or more by existing copper wireline technologies. Even if LAN technologies such as Ethernet over multiple dedicated twisted pair wiring or hybrid fiber/coax technologies such as cable modems are considered, it is impractical to backhaul at such data rates at these ranges (or at least without adding intermediate repeater equipment). Moreover, to the extent that such special wiring (i.e., CAT 5/6 or coax) is not presently available at a remote edge access network location; a new high capacity optical fiber is advantageously installed instead of a new copper connection.
Rather than incur the large initial expense and time delay associated with bringing optical fiber to every new location, it has been common to backhaul cell sites, WLAN hotspots, or LAN gateways from offices, campuses, etc. using microwave radios. An exemplary backhaul connection using the microwave radios 132 is shown in FIG. 1. Traditionally, such microwave radios 132 for backhaul have been mounted on high towers 112 (or high rooftops of multi-story buildings) as shown in FIG. 1, such that each microwave radio 132 has an unobstructed line of sight (LOS) 136 to the other. These microwave radios 132 can have data rates of 100 Mb/s or higher at unobstructed LOS ranges of 300 m or longer with latencies of 5 ms or less (to minimize overall network latency).
Traditional microwave backhaul radios 132 operate in a Point to Point (PTP) configuration using a single “high gain” (typically >30 dBi or even >40 dBi) antenna at each end of the link 136, such as, for example, antennas constructed using a parabolic dish. Such high gain antennas mitigate the effects of unwanted multipath self-interference or unwanted co-channel interference from other radio systems such that high data rates, long range and low latency can be achieved. These high gain antennas however have narrow radiation patterns.
Furthermore, high gain antennas in traditional microwave backhaul radios 132 require very precise, and usually manual, physical alignment of their narrow radiation patterns in order to achieve such high performance results. Such alignment is almost impossible to maintain over extended periods of time unless the two radios have a clear unobstructed line of sight (LOS) between them over the entire range of separation. Furthermore, such precise alignment makes it impractical for any one such microwave backhaul radio to communicate effectively with multiple other radios simultaneously (i.e., a “point to multipoint” (PMP) configuration).
In wireless edge access applications, such as cellular or WLAN, advanced protocols, modulation, encoding and spatial processing across multiple radio antennas have enabled increased data rates and ranges for numerous simultaneous users compared to analogous systems deployed 5 or 10 years ago for obstructed LOS propagation environments where multipath and co-channel interference were present. In such systems, “low gain” (usually <6 dBi) antennas are generally used at one or both ends of the radio link both to advantageously exploit multipath signals in the obstructed LOS environment and allow operation in different physical orientations as would be encountered with mobile devices. Although impressive performance results have been achieved for edge access, such results are generally inadequate for emerging backhaul requirements of data rates of 100 Mb/s or higher, ranges of 300 m or longer in obstructed LOS conditions, and latencies of 5 ms or less.
In particular, “street level” deployment of cellular base stations, WLAN access points or LAN gateways (e.g., deployment at street lamps, traffic lights, sides or rooftops of single or low-multiple story buildings) suffers from problems because there are significant obstructions for LOS in urban environments (e.g., tall buildings, or any environments where tall trees or uneven topography are present).
FIG. 1 illustrates edge access using conventional unobstructed LOS PTP microwave radios 132. The scenario depicted in FIG. 1 is common for many 2nd Generation (2G) and 3rd Generation (3G) cellular network deployments using “macrocells”. In FIG. 1, a Cellular Base Transceiver Station (BTS) 104 is shown housed within a small building 108 adjacent to a large tower 112. The cellular antennas 116 that communicate with various cellular subscriber devices 120 are mounted on the towers 112. The PTP microwave radios 132 are mounted on the towers 112 and are connected to the BTSs 104 via an nT1 interface. As shown in FIG. 1 by line 136, the radios 132 require unobstructed LOS.
The BTS on the right 104a has either an nT1 copper interface or an optical fiber interface 124 to connect the BTS 104a to the Base Station Controller (BSC) 128. The BSC 128 either is part of or communicates with the core network of the cellular network operator. The BTS on the left 104b is identical to the BTS on the right 104a in FIG. 1 except that the BTS on the left 104b has no local wireline nT1 (or optical fiber equivalent) so the nT1 interface is instead connected to a conventional PTP microwave radio 132 with unobstructed LOS to the tower on the right 112a. The nT1 interfaces for both BTSs 104a, 104b can then be backhauled to the BSC 128 as shown in FIG. 1.
In the conventional PTP radios 132, as described in greater detail in U.S. patent application Ser. No. 14/337,744 and incorporated herein, the antenna is typically of very high gain such as can be achieved by a parabolic dish so that gains of typically >30 dBi (or even sometimes >40 dBi), can be realized. Such an antenna usually has a narrow radiation pattern in both the elevation and azimuth directions. The use of such a highly directive antenna in a conventional PTP radio link with unobstructed LOS propagation conditions ensures that a modem within such radios has insignificant impairments at the receiver due to multipath self-interference and further substantially reduces the likelihood of unwanted co-channel interference due to other nearby radio links. However, the conventional PTP radio on a whole is completely unsuitable for obstructed LOS or PMP operation.
In U.S. patent application Ser. No. 14/337,744 and the related applications and patents summarized above, a novel Intelligent Backhaul Radio (or “IBR”) suitable for obstructed LOS and PMP or PTP operation is described in great detail in various embodiments of those inventions. When such IBRs (or other backhaul radios) are deployed in unlicensed or lightly licensed RF spectrum bands such as the Industrial, Scientific and Medical (or “ISM”) bands at, for example, 2.4-2.4835 GHz, the proposed Citizens Broadband Radio Service (or “CBRS”) band at, for example, 3.55-3.7 GHz, or the Unlicensed National Information Infrastructure (or “U-NII”) band at, for example, various sub-bands within 5.15-5.925 GHz, then performance of such backhaul radios may be significantly impacted by both self-interference from other such backhaul radios and from uncoordinated interference by other transmitting devices. Such uncoordinated interference sources may include government radars, wireless local area networking devices compatible with the IEEE 802.11 family of standards (or “WiFi” devices), or cordless telephones. Backhaul radios such as IBRs can advantageously mitigate the effects of such interference by exploiting the frequency, time, spatial and cancellation domains. In an exemplary backhaul radio embodiment, an IBR determines instantaneous frequency, time, spatial and cancellation domain interference mitigation techniques using a radio resource controller (or “RRC”) as also described in U.S. patent application Ser. No. 14/337,744 and the related applications and patents summarized above. However, previously known techniques for determining and implementing the specific radio resource selections have at least the significant deficiency that such techniques do not account for simultaneous resource allocation across multiple of these domains and for determining the optimal arrangement of such resources while simultaneously maintaining one or more high throughput and low latency backhaul links. Thus, there is a need in the art for developing backhaul radios that will select radio resources that provide high throughput, low latency and robustness to interference in consideration of multiple aspects of the frequency, time, spatial and cancellation domains in order to maximize the link performance of backhaul radios in the presence of self-generated and uncoordinated interference sources.
For example, in conventional PTP radios, spatial and cancellation domain optimization is not available at all. In addition, such conventional PTP backhaul radios do not have resources that enable such radios to simultaneously deliver high throughput link performance and determine interference across the remaining frequency and time domains. At deployment, such conventional radios are typically set in a scan mode with the desired link offline at the radio receiver such that a user can manually determine which channels within an applicable RF band have the least amount of interference during an observation period. The user then selects a frequency channel of operation for the instant receiver within the backhaul link and such channel is used unless another user-initiated scan is made again in the future. Thus, the conventional PTP backhaul radio art does not disclose backhaul radios that will select radio resources that provide high throughput, low latency and robustness to interference in consideration of multiple aspects of the frequency, time, spatial and cancellation domains in order to maximize the link performance of backhaul radios in the presence of self-generated and uncoordinated interference sources.
For example, U.S. Pat. No. 8,462,709 discloses methods for interference measurements. However, the techniques described in U.S. Pat. No. 8,462,709 are applicable specifically to WiFi and to detection of WiFi interference in a 40 MHz channel. In contrast, for exemplary embodiments of the present invention, interference detection is performed while maintaining full link capacity, and includes detection of a multitude of signal types, including WiFi, self-interference from other backhaul radios, and unknown sources. In some exemplary embodiments, the band over which interference is measured by this invention can comprise numerous such channels each of 40 MHz or other channel bandwidth.
For example, U.S. Pat. No. 8,737,308 discloses methods to measure interference on alternate radio frequency (RF) channels. However, the methods in U.S. Pat. No. 8,737,308 are applicable to cellular systems with one device measuring interference. In contrast, for exemplary embodiments of the present invention, interference detection is performed on two transceivers within a link simultaneously, and both transceivers are also utilized for data transmission simultaneously. Thus in exemplary embodiments herein, data transmission and reception is maintained while making the interference measurements, which the prior art does not account for.